Polymer-matrix composites offer unique combinations of properties and are useful in a wide range of applications. Such composites may be fabricated utilizing either thermosetting or thermoplastic polymer matrix materials with a variety of particulate or fibrous fillers or reinforcements. It is generally advantageous to have strong adhesion between the polymer matrix material and the surfaces of the various particulate or fibrous substrates and there is considerable art related to substrate finishes and other treatments to optimize adhesion to polymer matrices. For example, in the production of long-fiber reinforced composites, improved adhesion between the polymer matrix and the fiber reinforcement leads to increased material performance. Good adhesion is particularly important where failures are likely to occur by delamination or by other adhesive failure modes.
As described in, for example, U.S. Pat. Nos. 5,840,238, 6,310,121, and 6,525,125, the disclosures of each of which are incorporated herein by reference, polymers generated by olefin metathesis processes are attractive as composite matrix materials. Of particularly beneficial use are the polymers generated by the ROMP of cyclic olefins. The low viscosity of cyclic olefin resin formulations and the ability to control ROMP kinetics (e.g., U.S. Pat. Nos. 4,708,969 and 5,939,504, the disclosures of both of which are incorporated herein by reference) facilitate composite processing and manufacture, and the corrosion resistance and high toughness of ROMP polymers leads to good composite durability. Additionally, certain properties of ROMP polymers, e.g., mechanical strength and stiffness, heat distortion temperature and solvent resistance, can be further enhanced by crosslinking induced via thermal treatment (e.g., U.S. Pat. No. 4,902,560, the disclosure of which is incorporated herein by reference) or chemically by addition of peroxides (e.g., U.S. Pat. No. 5,728,785, the disclosure of which is incorporated herein by reference).
Commercially important ROMP resin formulations are generally based on readily available and inexpensive cyclic olefins such as dicyclopentadiene (DCPD), norbornenes, cyclooctadiene (COD), and various cycloalkenes. However, in contrast to traditional resin systems (e.g., epoxy, acrylate, urethane, and polyester resins) based on polar functional group chemistries, these nonpolar ROMP resins have poor intrinsic adhesion to the relatively polar surfaces of common carbon, glass, or mineral fillers and reinforcements. The addition of various silanes to such resin formulations for improvement of electrical and mechanical properties of ROMP polymers is described in U.S. Pat. Nos. 5,840,238, 6,001,909, and 7,339,006, the disclosures of each of which are incorporated herein by reference. Many widely used commercial silanes do not give optimal properties with ROMP polymers, however, and the greatest enhancements are only obtained when the silanes comprise groups with high metathesis activity (the relative reactivity of various metathesis active groups is described in J. Am. Chem. Soc., 2003, 125, 11360-11370).
As described in International Patent Application Number PCT/US12/42850, the disclosure of which is incorporated herein by reference, it was discovered that the addition of an adhesion promoter comprising a compound containing at least two isocyanate groups to a cyclic olefin resin formulation (e.g., ROMP resin formulation) provides beneficial improvements in the adhesion of a cyclic olefin resin formulation to substrate materials, such as, for example carbon and glass reinforcement materials.
According to International Patent Application Number PCT/US12/42850, addition of an adhesion promoter comprising a compound containing at least two isocyanate groups to a cyclic olefin resin formulation, where the resin formulation comprising the adhesion promoter was contacted with an olefin metathesis catalyst and used to manufacture ROMP polymer-matrix composites, provided improved adhesion of ROMP polymer matrices to composite substrate materials compared to ROMP polymer matrices without such adhesion promoters. Adhesion of the ROMP polymer-matrices to substrate materials was measured by the short beam shear method according to ASTM D2344. Interlaminar shear strength (ILSS) is a measure of the adhesion and/or compatibility between the polymer matrix and the substrate material in a composite.
In addition, International Patent Application Number PCT US12/42850 also demonstrated that the addition of at least one compound comprising a heteroatom-containing functional group and a metathesis active olefin (e.g., 2-hydroxyethyl bicyclo[2.2.1]hept-2-ene-5-carboxylate (HENB)) to a cyclic olefin resin formulation (e.g., ROMP resin formulation) comprising at least one cyclic olefin and an adhesion promoter comprising at least one compound containing at least two isocyanate groups, where the resin formulation comprising the adhesion promoter was contacted with an olefin metathesis catalyst and used to manufacture ROMP polymer-matrix composites, further improved the efficacy of the adhesion promoter to effectuate adhesion between the ROMP polymer-matrix and the composite substrate material.
While International Patent Application Number PCT/US12/42850 demonstrated that compounds containing at least two isocyanate groups are effective to improve the adhesion of cyclic olefin resin formulations to substrate materials (e.g., carbon and/or glass substrate materials), the in-resin storage stability of adhesion promoters comprising at least one compound containing at least two isocyanate groups was not addressed. Furthermore, the in-resin storage stability of adhesion promoters comprising at least one compound containing at least two isocyanate groups, where the cyclic olefin resin formulation (e.g., ROMP resin formulation) further comprises at least one compound comprising a heteroatom-containing functional group and a metathesis active olefin was also not addressed.
The importance of using additives in resin formulations, particularly cyclic olefin resin formulations, where the additives possess in-resin storage stability is known in the art. For example, U.S. Pat. No. 4,943,621 discloses the importance of using storage stable additives possessing in-resin storage stability, particularly storage stable co-catalysts, as components in cyclic olefin resin formulations. Moreover, preparing cyclic olefin resin formulations which comprise additives having in-resin storage stability is of particular importance in the commercial manufacturing of polymer articles and/or polymer-matrix composites manufactured from such cyclic olefin resin formulations. For example, for a manufacturer of cyclic olefin resin formulations to successfully commercialize such resin formulations it is necessary to be able transport and store the resin formulations prior to use, which further necessitates the need for the use of in-resin storage stable additives and components. Furthermore, it is preferable, particularly from a commercial perspective, that the cyclic olefin resin formulations be provided to customers, molders, and other end-users with all of the necessary additives and components contained in the cyclic olefin resin formulation so that these individuals can avoid additional processing and therefore use the resin formulations as received to manufacture articles comprising ROMP polymers and/or ROMP polymer-matrix composites.
After further investigation into the in-resin storage stability of adhesion promoters comprising compounds containing at least two isocyanates, the inventors have discovered that such adhesion promoters do possess in-resin storage stability, particularly where the resin is a cyclic olefin resin. The in-resin storage stability of adhesion promoters comprising compounds containing at least two isocyanates, particularly where the resin is a cyclic olefin resin is demonstrated and discussed infra. Surprisingly, however, the inventors have discovered that when a compound comprising a heteroatom-containing functional group and a metathesis active olefin (e.g., 2-hydroxyethyl bicyclo[2.2.1]hept-2-ene-5-carboxylate (HENB)) is independently or separately added to the cyclic olefin resin formulation containing an adhesion promoter comprising a compound containing at least two isocyanates, the in-resin storage stability of the adhesion promoter is adversely affected as observed by a decrease in the ILSS of polymer-matrix composites, the results of which are demonstrated and discussed infra.
Despite the advances achieved in the art, particularly in the properties of olefin metathesis polymers (e.g., ROMP polymers and ROMP polymer-matrix composites) and their associated applications, a continuing need therefore exists for further improvement in a number of areas, including the manufacture of cyclic olefin resin formulations, in particular ROMP resin formulations, for use in the manufacture of ROMP polymer-matrix composites, where such composites possess strong adhesion between the polymer matrix and substrate material (e.g., carbon and/or glass reinforcement materials) Furthermore, there also exists a need for further improvement in the manufacture of cyclic olefin resin formulations, in particular ROMP resin formulations, where the formulation additives and components, particularly adhesion promoters, possess in-resin storage stability.